Pulling off the biggest win in her MMA career, Michelle Waterson won the Invicta Fighting Championship's atomweight championship in a thrilling victory over Jessica Penne on Friday during Invicta FC 5.

"Karate Hottie" Waterson was a notable underdog in the match, giving up several inches in arm- and leg-length against the dangerous Penne.

Throughout the match, Penne put Waterson in trouble multiple times with various submissions and some heavy striking, beating down on her undersized opponent at several intervals.

Waterson nearly lost the bout in Round 3, as Penne managed to sink in an extremely tight armbar attempt with her challenger completely exposed on her back.

Photo Credit: Bikini.com

But Waterson refused to tap, instead letting her arm pop in and out of position, surviving to the third round and eventually making her comeback with a submission of her own.

Just under three minutes into the fourth round, Waterson managed to grab Penne with a strong armbar, tightening up the hold in a split-second motion. Penne quickly tapped, giving Waterson the hard-fought win.

Once referee John McCarthy stopped the bout, an incredibly happy Waterson broke down in tears, huddled over in wracking sobs before celebrating with famed MMA coach Greg Jackson.

As a visibly dejected Penne looked on, Waterson gave a tearful post-fight interview, pouring her heart out after Invicta FC president and founder Shannon Knapp placed a brand-new Invicta title belt around the champion's waist:

You just can't quit. Even when you feel like you can't go on. Jessica Penne is a f***ing awesome fighter, and I really want to thank her for thanking the fight.

You just gotta believe in yourself. Don't let nobody take that away from you. Throughout my whole training camp, I had to tell myself I could hang with her, that I could push back. It was a great fight.

Waterson's win marks a fifth straight victory on her 11-3 professional MMA record, as well as her first-ever MMA world championship.

Competing in various martial arts practices (karate, muay Thai, wushu) over the years, Waterson is a seasoned veteran of several regional MMA promotions, including Ring of Fire, King of the Cage and Strikeforce.

Along with her combat sports background, the Colorado native is also notable for her modeling work.

Moreover, Waterson has also solidified herself one of the best female MMA fighters in the world, with Jessica Penne losing just a handful of months after first capturing the Invicta atomweight title against formerly undefeated Jewels featherweight champion Naho Sugiyama of Japan.

McKinley Noble is an MMA conspiracy theorist. His work has appeared in NVision, PC World, Macworld, GamePro, 1UP, MMA Mania & The L.A. Times.